The determination of electrochemical reactivity and sustainability on individual hyper-stoichiometric UO2+x grains by Raman microspectroscopy and scanning electrochemical microscopy

Using scanning electrochemical microscopy and Raman microspectroscopy, we have successfully observed four distinct defect structures in hyper-stoichiometric UO2+x and demonstrated the relationships between the defect structures and their ability to sustain cathodic reduction processes. When only random point defects are present, the initially inert surface is enhanced by oxidation of the UO2+x. However, when the UO2+x is already extensively oxidized and cuboctahedral clusters are present, further oxidation reduces the surface reactivity. At intermediate levels of stoichiometry corresponding to Willis clusters the surface appears to be reversibly oxidizable.